Motor vehicle air filter systems are used to remove impurities such as sand particles and water from the air which is required by an internal combustion engine. The intaken air is routed by way of an inlet tube into the housing of an air filter where it first sheds larger particles and water droplets. The air which has been precleaned in this way is then intaken through a filter element and travels by way of an outlet tube to the internal combustion engine. Both the air filter housing and also the inlet and outlet tube consist of relatively stiff components in order to withstand the negative pressure generated within the air filter system by the suction action of the internal combustion engine.
The water which is formed in the filtration of air must be removed from the air filter housing against this negative pressure. For this purpose it is brought together in a collecting region on the bottom of the housing. In the collecting region there is a drain which, however, is closed by a valve to prevent air from flowing into the housing through the drain due to the negative pressure which prevails in the filter housing. With a rising water level in the collecting region, i.e., with increasing geodetic height of the water column located over the valve, the water pressure which acts on the valve of the drain rises until it finally equalizes the negative pressure and the valve is pushed open.
The water which is then running out is routed by way of a drain hose underneath the filter housing in the engine compartment into a region where it can freely drip out. It is also possible to arrange the valve on the exit end of the hose. This results in that the water is collected within the hose and thus a separate collecting region on the bottom of the housing can be dispensed with. The water collecting in the comparatively narrow tube also ensures that the water does not slosh as the motor vehicle is driving, by which splash water could be thrown onto the filter element of the air filter.
Instead of a valve for preventing the inflow of air through the drain hose, according to DE 199 42 503 A1 the drain hose is installed in the form of a loop, or meandering. In the resulting turns of the drain hose, according to the siphon principle there is always a minimum amount of water which is moved due to the negative pressure in the filter housing within the drain hose, but which prevents entry of air through the drain hose into the filter housing as in the case of the valve. However, this form of air sealing presupposes a relatively small cross section of the drain hose, since otherwise air bubbles could rise through the water column which has been displaced due to the negative pressure in the drain hose and for this reason the desired sealing function would not be achieved.
Since the drain hose is always attached to the bottom of the filter housing, in the production or repair of a motor vehicle the problem is that the drain of the air filter housing is only poorly accessible for a mechanic, since the air filter has already been installed in the engine compartment of the motor vehicle. Thus, there is the risk that the drain hose will be kinked or pinched between other components in assembly such that water can no longer drain out of the filter housing by way of the drain hose. Due to the unfavorable location of the connection for the drain hose, after assembly it is also difficult to check the proper position of the drain hose under the air filter.
Therefore, the object of this invention is to enable smooth assembly of a drain hose for the collected liquid for a motor vehicle air filter system and thus to ensure proper alignment of the hose.